The present invention relates generally to a lock-up device. More specifically, it relates to a lock-up device for a torque converter.
Generally, a torque converter can accelerate or decelerate an automobile smoothly because it transmits power by the agency of a fluid. However, such disadvantages as inefficient fuel consumption and energy loss due to fluid slip can stem from torque converters.
Therefore, some conventional torque converters have a lock-up device disposed between the input-side front cover and the turbine connected to the output shaft. The lock-up device includes a piston which is pressed against the front cover by hydraulic drive in order to transmit power directly. Owing to the difficulty of transmitting a large torque to the output-side member only through the contact of the piston against the front cover, one type of lock-up device has been developed which has a plurality of friction discs provided between the front cover and the piston in order to improve torque transmission capability.
When this type of lock-up device is in engagement, the piston, under hydraulic power, and the front cover sandwich the friction discs, pressing the friction discs against each other. Consequently, the torque of the front cover is transmitted to the piston through the friction discs, thereby to rotate the output shaft.
When the lock-up device is in disengagement, the friction discs, which should remain spaced apart from one another, are forced toward the piston due to the flow of hydraulic fluid through the gaps between the piston and front cover. Consequently, the friction members and the piston come into contact, transmitting the rotation of the front cover to the piston through the friction members, and creating a drag torque in the output shaft.